There is growing interest in image retrieval such as would be encountered, for example, in an image search on the World Wide Web because of the limitations inherent in metadata-based systems. Presently most image searches are conducted by searching using keywords. This requires that images be located by matching the keywords in a search query to metadata associated with an image. This type of a search requires mechanisms (such as human labeling) that can describe every image via metadata which is impractical for very large databases, or for images that are generated automatically, such as, for example, from surveillance cameras.
Another reason image search, such as searching for images on the World Wide Web, is difficult is in part because a handful of keywords are generally insufficient for characterizing the visual properties of an image, such as, for example, that an image with vertical lines in it is sought. Popular search engines have begun to provide a set of automatically generated meta tags based on simple characteristics of images (such as tags for black and white images or images that contain a face), but such approaches are limited by the fact that it is unclear what tags end-users want to be able to use in examining Web image search results.